1. Field of the Invention
The present invention relates to an endoscope apparatus including an electronic image pickup unit at a distal end portion of an insertion portion.
2. Description of the Related Art
Conventionally, in, e.g., a medical field, in order to observe a site inside a subject where visual observation is difficult, such as an inside of a living body, an endoscope including an electronic image pickup unit for observing an optical image at a distal end portion of an insertion portion is used. The electronic image pickup unit includes, for example, an objective lens and an image pickup device such as a CCD (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) sensor disposed at a plane on which an image from the objective lens is formed.
In recent years, for endoscope apparatuses of this type, enhancement in performance of an image pickup device and an increase in definition of picked up images, which is realized by an increase in output of illuminating light, have been promoted. However, for example, where performance of an image pickup device is enhanced, the amount of heat generated from the image pickup device and, e.g., various electronic components attached thereto. Furthermore, where the output of illuminating light is increased, the amount of light irregularly reflected inside the illumination optical system increases, and a majority of irregularly-reflected light is transformed into heat inside the distal end portion. Furthermore, if the heat remains inside the distal end portion, what is called temperature noise may occur in the image pickup device, resulting in image deterioration.
In response to such problems, for example, Japanese Patent Application Laid-Open Publication No. 2001-299677 discloses a technique in which a holding member that includes a stainless steel material having good thermal conductivity is housed inside a first outer case that includes a stainless steel material having good mechanical endurance and good chemical endurance (chemical resistance), an electronic image pickup unit (e.g., a light-receiving lens and a CCD) is inserted in an inner space of the holding member and a plurality of LEDs are disposed as a light source at positions surrounding the light-receiving lens at a front end face of the holding member. In the technique in Patent Literature 1, the holding member is formed using a material having high thermal conductivity, and an outer peripheral face of the holding member is brought into direct contact with an inner circumferential face of the thin-walled first outer case, whereby heat generated in the plurality of LEDs is transferred through the holding member and efficiently released to the outside from the first outer case.